A gunman opened fire at a South Florida high school today, killing 17 people and sending students running for their lives, according to law enforcement officers on the scene.

-- The suspect, 19-year-old Nikolas Cruz, was taken into custody off campus. He slipped out of the school after the shooting by blending in with other students who were trying to escape, according to two law enforcement sources and an eyewitness.

-- Cruz had "countless magazines" and was believed to have an AR-15 rifle, the sheriff said.

-- The sheriff said Cruz had attended the school but was expelled for disciplinary reasons.

-- Students were seen sprinting out of the school with their hands up as authorities with guns drawn swarmed the area. Other students were seen lined up one by one, leaving the area in an orderly fashion. Some students were hysterical, reported ABC affiliate WPLG.

John McCall/South Florida Sun-Sentinel via AP

Medical personnel tend to a victim following a shooting at Marjory Stoneman Douglas High School in Parkland, Fla., on Feb. 14, 2018.

John McCall/South Florida Sun-Sentinel via AP

Medical personnel tend to a victim following a shooting at Marjory Stoneman Douglas High School in Parkland, Fla., on Feb. 14, 2018.

Joel Auerbach/AP

Women embrace in a waiting area for parents of students after a shooting at Marjory Stoneman Douglas High School in Parkland, Fla., Feb. 14, 2018.

Student Michael Katz told ABC News that at the end of the day he "heard what sounded like a garbage truck like banging."

"If you see something, say something," Israel said at a news conference earlier today. "If anybody has any indicator that someone's going through a behavioral change, on social media if there are disturbing photos, perhaps bombs or firearms or just videos or pictures that are just not right, please make sure law enforcement knows about it."

On Wednesday evening, a large law enforcement presence consisting of both the Broward County Sheriff's Office and Palm Beach County Sheriff's Office was spotted at the Lantana Cascade Mobile Home Park in Lake Worth. WPBF reported it may be related to the school shooting.

WPLG

Nikolas Cruz, the suspect in a shooting at Marjory Stoneman Douglas High School in Parkland, Fla., is escorted out of a hospital and into a police car.

Israel said this evening officials were still working to identify the victims. He said a football coach was among the dead.

ABC News

A map shows the location of Marjory Stoneman Douglas High School in Parkland, Fla.

Pierre Jospitre said he was pulling into his driveway from work when he saw the suspect on the ground with an official on top of him.

Within seconds, several law enforcement officers swarmed the area, Jospitre said, adding that when the suspect was picked up off the ground, he was vomiting and was not walking right.

The school will be closed for the rest of the week, Broward County Public Schools announced Wednesday night. There are over 3,000 students at the school, according to its website. Broward County Public Schools superintendent said grief counselors would be available.

President Donald Trump tweeted, "My prayers and condolences to the families of the victims of the terrible Florida shooting. No child, teacher or anyone else should ever feel unsafe in an American school."

My prayers and condolences to the families of the victims of the terrible Florida shooting. No child, teacher or anyone else should ever feel unsafe in an American school.